System of distribution



W. A. PRESSEY.

SYSTEM OF DISTRIBUTION.

APPLICATION FILED APR.23, 1920.

'1,373,9 1 O. Patented Apr. 5, 1921.

. Fig.2. ea 29 2a 29 2a 27 v FL I I u ,2, [I 2 5 7 [1/ 3' T LII I 28 2828 Inventor:

Wilbur A.'Pr-'esse WWW His Attorney.

WILBUR A. PRESSEY, OE BOSTON, MASSACHUSETTS, ASSIGNOR TO GENERALELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

SYSTEM OF DISTRIBUTION.

Specification of Letters Patent.

Patented Apr. 5, 1921.

Application filed April 23, 1920. Serial No. 375,973.

tribution and more particularly to an alternating current polyphasesystem wherein the load is of such a character that it 1s necessary totransform the voltage of the source.

In such polyphase alternating current systems of distribution it isfrequently necessary to Vary slightly the ratio of transformation fromthe source to the load, in order to take care of variations in linedrop, or

other conditions necessitating the same remedy. Especially is this trueof systems in which the source has a comparatively high E. M. F.transformed to a comparatively low E. M. F. for supplying the load. Insystems of this character, the load, being a variable uantity, and beingconnected t9 the secon ary or low voltage side of the transformingapparatus may at times increase to such an extent that there is supplieda relatively heavy current over the conductors carrying the load; andthus there is caused an appreciable impedance drop at the point wherethe load is supplied. To maintain the voltage constant at this point itis necessary to increase the voltage at the source as the loadincreases, and on the other hand to decrease the voltage at thesourcewhen the load decreases. In systems heretofore used it has beennecessary to disconnect the load entirely and thus interrupt the servicewhile the voltage adjustments were being made at the transformer. It isone of the objects of my invention to make it possible to vary thevoltage supplied to the load circuit without interrupting the service.Another object of my invention is to insure the proper sequence ofoperation so that no serious unbalancing of the polyphase system mayresult. Another obje'ctof myinvention is to provide simple andinexpensive means for performing the various steps. Other objects andadvantages of my invention will be apparent as the description proceeds.

The construction and mode of operation of my invention may be understoodby reference to the accompanying drawings, in Whlch F lgure 1 shows thecomplete wiring (Ila-gram of the entire system, and particularly how thetransforming apparatus is connected both to the source and to the load;and Fig. 2 is a view showing more in detail the apparatus for insuringproper sequence of operation for varying the voltage, and for theprevention of appreciable unbalancing.

Referring now more in detail to the drawin s, in which like referencecharacters refer to like parts throughout, I show a source of polyphasealternating current, in this case the three-phase mains 11, 12 and 13.This source of alternating current, after its voltage is appropriatelytransformed, supplies the load designated by the numeral 26. Thetransforming apparatus in this case consists of a plurality of primaryand secondary coils, each primary coil being inductively associated withits corresponding secondary coil and so related to the other coils thatall of them form a polyphase trans forming system. These coils may bearranged to form independent single-phase transformers, or else arrangedon a single core to form one polyphase transformer. The primary coils14, 15 and 16 are connected in any appropriate fashion to the mains 11,12, and 13; these coils are shown in the present instance as deltaconnected. Each secondary coil is made up in this case of two parts,although a single part may be used as well. These secondary coils arethus made up of the coil sections 17, 18, 19, 20, 21 and 22connectedtogether in as shown. Appropriate means are provided forvarying the effective turns of the secondary coils of the transformers.In this case the means for accomplishing this result are convenientlyinserted between the pairs of coil sections and comprise plugs andreceptacles for varying the number of turns in the secondary coils byconnecting any one of a plurality of taps on one coil section to any ofthe taps on the other coil section. The secondary coils are connected indelta by means of appropriate switching devices.

23, 24 and 25, which switching devices are so arranged that by openingany one of them, one of the secondary coils 1s disconnected entirelyfrom the closed delta conof the secondary coils by small incrementsrendered inactive.

comprise a plurality of receptacles and a plug adapted to makeelectrical contact therein for controlling the tap change of the coils.While in this case the plugs and receptacles are adapted to make directcontact with the taps, it is evident that appropriate relay means may beused to accomplish the same result, if such be necessary. Receptacles 1,2, 3, land 5 are arranged to cooperate with a plug to control the numberof turns of the secondary coil comprisin the two sections 17 and 18; thereceptac es 1, 2', 3', 4c-'and 5 cooperate in the same way with thesecondary 'coil comprising the sections 19 and 20; and receptacles 1",2", 3", 4" and 5" likewise cooperate in the same way with the secondarycoil comprising the sections 21 and 22. In this instance, three taps aretaken .from each left-hand coil section and two from each right handcoil section. The two coil sections are connected in series by means ofthese taps through one or other of the receptacles and the cooperatingplug. The taps are located in such a way that by inserting the plugsuccessively in receptacles l to 5 a decrease of voltage isaccomplishedof say about 2%% of normal voltage for each plug change.sorted in receptacles 1,'all of the turns in section 17-18 are active,as may be readily verified by tracing the wiring. However, when the plugis' withdrawn from receptacle 1 and inserted in receptacle 2, some ofthe turns of the left hand coil 17 are rendered inactive, the number ofturns being in this case equivalent to about 2 of the whole number inboth of the coils 17 and 18.

When the plug is withdrawn from receptacle- 2 and inserted inreceptacle'B, all of the turns in the left hand coil are renderedactive, but in the right hand coil 18 a number.

of turns approximating double the number of turns between ta changes oncoil 17 are en the plug is withdrawn from receptacle 3 and inserted inreceptacle 4, some turns are again rendered inactive on the left handcoil 17 inaddition to the turns that are already inactive on the righthand coil 18. When the plug is with: drawn from receptacle 4 andinserted in receptacle 5,. the minimum E. M. F. is ob- Thus when theplug is in-* tained, since another small section of turns is renderedinactive on the secondary coil 17. As regards the secondary coilcomprising sections 19 and 20 and their associated receptacles 1 to 5,it is seen that precisely the same effect is obtained in this case as inthe case just considered, as the plug is grad.- ually moved fromreceptacle 1 to receptacle 5, and likewise precisely the same efiect isobtained for the third secondary coil comprising sections 21 and 22 whena plug is moved by single steps from receptacle 1" to receptacle 5". Tovary the ratio of transformation, therefore, it is merely necessary toopen any one of the switches 23, 24 and 25, and while any one of theseswitches is open, to adjust the plug in the receptacles associated withthe secondary coil controlled by the open switch, then to close theswitch 1 and to do this successively with both of the other switches. Itwill be noted that while this operation is being carried on the serviceis uninterrupted.

It is a necessary outcome of the uninterrupted supply to the load thatthe system of E. M. F.s obtained from the secondary coils of thetransforming apparatus becomes slightly unbalanced while the voltage isbeing adjusted. This is due to the fact that but one secondary coil canbe adjusted at a time. To prevent excessive or appreciable Iunbalancing, which mightresult in objeccomprising the two sections 17and 18, we .can withdraw the plug from receptacle 1 .and insert it intoreceptacle 2, but before .we can remove the plug from receptacle 2 andinsert it into receptacle 3, it is necessary that both of the otherplugs for the remaining secondary coils must be in receptacles 2' and2". After all of the plugs are in the proper receptacles so that abalanced.

voltage is obtained, a further shift of the plugs may be accomplished.In this way ut one step at a time may be taken throughout all of thesecondary coils and no greater unbalancing can take place in the voltagethan that represented by the movement of the plug from one receptacle toan adj acent one. i

The means that I employ to accomplish this desirable result is aninterlocking bar 27,

-. which is clearly shown in Fig. 2. This interlocking bar 27 is adaptedto be moved 'we start in, say, with the secondary coil lengthwise and isguided in-its movementby appropriate metal clips 28. The interlockingbar is provided with a plurality of apertures 29 just large enough touncover two adjacent receptacles such as receptacles 1 and 2,receptacles 1 and 2 and receptacles 1 and 2", as shown in Fig. 2. Thenumber and arrangement of these apertures 29 depend upon the location ofthe receptacles and also upon whether the system is three-phase,four-phase, five-phase, etc. When the bar 27 is in its extreme left handposition, the receptacles 1 and 2 are uncovered as well as thereceptacles 1' and 2 and 1" and 2". Suppose now that the three plugs arein receptacles 1, 1' and 1". 'In order to decrease the secondary Voltageby a small increment, we may start in for example with the plug inreceptacle 1 and move it into receptacle 2. We cannot now remove theplug from receptacle 2 and insert it into receptacle 3 because the barcovers up this receptacle and it cannot be moved to uncover thisreceptacle while there are plugs in receptacles 1' and 1", said plugsblocking the movement of bar 27. Therefore, the next step after removingthe plug from receptacle 1 to receptacle 2 is to remove the plug fromreceptacle 1' or 1" and insert it into receptacle 2 or 2", and repeatingthis process with the remaining plug. The bar 27 may now be moved to theright a distance corresponding to the distance between two adjacentreceptacles and the process repeated. In this way appreciableunbalancing of the polyphase system is prevented, since there can be nogreater unbalancing at any onetime, than is represented by the movementof the plug from one receptacle to its adjacent one. My interlocking bartherefore comprises a relatively simple means for insuring the propersequence of operation of the tap changing scheme.

For a clear understanding of the mode of operation of my invention, itis perhaps appropriate at this point to review briefly the method ofoperation of the entire system, to vary the voltage supplied to the load26. We will say that the switch 24 is opened first. The load is nowbeing operated on open delta supplied by the secondary coils comprisingsections 1718 and sections 2122. The secondary coil comprising sections1920 is entirely disconnected from the system. The plug is moved fromany of the receptacles 1' to 5 to an adjacent receptacle. The switch 24is now closed. At this stage of the operation there is a slightunbalancing of the voltage system. The next step is to open either oneof the two remaining switches 23 and 25. Suppose the switch 23 beopened. If this be done, the load is again operated on open deltasupplied by the secondary coils made up of sections 19, 20 and. 21, 22.The secondary coils comprising sections 17-18 is entirely disconnectedfrom the system. The plug is moved from one of the receptacles l to 5 toan adjacent one in the same direction as the plug first referred to. Theswitch 23 is now closed, and switch 25 opened and the plug shifted inthe same direction as in the two previous instances to an adjacentreceptacle. The switch may now be closed. Should a further variation inload be necessary, the interlockin bar 27 is shifted either to the rightor to t e left so as to uncover the next receptacle of each set intowhich the plugs are to be inserted. Then the entire sequence-ofoperation as set out above is again performed. This is carried on untilthe E. M. F. of the secondary side of the system is varied to therequired amount.

While I have shown in the accompanying drawing the preferred embodimentof my invention, I do not desire to be limited thereto, but aim to coverin the appended claims all modifications falling fairly within the scopeof my invention.

What 'I claim as new and desire to secure by Letters Patent of theUnited States, is:

1. In a system of distribution comprising a source of polyphasealternating current, a plurallty of primary and secondary coils fortransformingthe voltage of said source, the

secondary coils being connected in closed delta for supplying a load,the method of varying the ratio of transformation without disconnectingthe load, which consists in opening the delta by disconnecting one ofsaid coils therefrom, varying the number of turns on said coil,reconnecting said coil into the delta, and repeating this operation insuccession with eachsecondary coil.

2. In a system of'distribution comprising a source of polyphasealternating current and a plurality of primary and secondary coils fortransforming the voltage of said source, the secondary coils beingconnected in closed delta for supplying a load, the method of varyingthe secondary voltage without disconnecting the load, which con methodof varying the ratio of transforma tion in a plurality of steps, whichconsists in opening the delta by disconnecting one of said secondarycoils therefrom, varying the number of turns on said coil by arelatively small amount, reconnecting said coil into the delta,performing this operation in succes- 'sion with each secondary coil, andrepeating this process until the required change in voltage is obtained.

4. In a system of distribution, in combination, a source of polyphasealternating current, a plurality of primary and secondary coils fortransforming the 'voltageof said source, the secondary coils beingconnected in closed delta for supplying a load, means for varying theratlo of transformat on without disconnecting the load, comprising meansfor disconnecting each of said secondary coils from the delta, means forvarying the number of turns on said coils, and means for preventing an apreciable unbalancing of the system while t e who of transformation isbeing adjusted.

5. In a system of distribution, in combination, a source of polyphasealternating current, a plurality of primary and secondary coils fortransforming the voltage of said source, the secondary coils beingconnected in closed delta for supplying a load, means for varying thesecondary voltage in a plurality of steps without isconnecting the load,comprising means for disconnecting each of said secondary coilstherefrom in regular sequence, means for varying the number of turns onsaid coils and means for araeao insuring that all of the coils havetheir turns varied b an e ual small increment before a for varying theratio of transformation without disconnecting the load','comprisingswitches for disconnecting each of said secondary coils from the delta,a plurality of taps for each secondary coil for varying the number ofactive turns thereof, plugs and receptacles for controlling the tapconnections, and an interlocking bar cooperating with said plugs andreceptacles to insure that all of the coils have their turns varied byan equal, small increment before a further variation can be efl'ected,whereby appreciable unbalancing of the secondary voltages is obviated. I

- In witness whereof, I have hereunto set my hand this twentieth day ofApril 1990.

WILBUR A. ranssnv.

